Iron(III) complexes of 1,2-di(imino-4′-antipyrinyl)ethane

Article abstract of DOI:10.1081/SIM-100107711

Iron(III) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)ethane (L) have been prepared and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. The complexes have the general formula [Fe(L)(ClO₄)](ClO₄)₂ and [Fe(L)X₂]X (X=NO₃, SCN, Cl or Br). L acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate complex, one of the perchlorate ions is coordinated bidentately while in the nitrate and thiocyanate complexes two of the anions are coordinated monodentately to the metal ion. In the chloride and bromide complexes, two of the halide ions are coordinated. A high-spin octahedral geometry is assigned around Fe(III) in all of these complexes.

Full text of DOI:10.1081/SIM-100107711

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IRON(III) COMPLEXES OF 1,2-DI(IMINO-4′-
ANTIPYRINYL)ETHANE
N. T. Madhu a & P. K. Radhakrishnan b
a School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills PO,
Kottayam, Kerala, 686 560, India
b School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills PO,
Kottayam, Kerala, 686 560, India
Version of record first published: 15 Aug 2006.
To cite this article: N. T. Madhu & P. K. Radhakrishnan (2001): IRON(III) COMPLEXES OF 1,2-DI(IMINO-4′-
ANTIPYRINYL)ETHANE, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 31:9, 1663-1673
To link to this article: http://dx.doi.org/10.1081/SIM-100107711
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(9), 1663±1673 (2001)
IRON(III) COMPLEXES OF 1,2-DI(IMINO-
40-ANTIPYRINYL)ETHANE
N. T. Madhu and P. K. Radhakrishnan*
School of Chemical Sciences, Mahatma Gandhi
University, Priyadarshini Hills PO, Kottayam-686 560,
Kerala, India
ABSTRACT
Iron(III) complexes of the Schi€ base 1,2-di(imino-40-anti-
pyrinyl)ethane (L) have been prepared and characterized by
elemental analyses, electrical conductance in non-aqueous
solvents, infrared and electronic spectra as well as magnetic
susceptibility measurements. The complexes have the general
formula [Fe(L)(ClO4)](ClO4)2 and [Fe(L)X2]X (XˆNO3,
SCN, Cl or Br). L acts as a neutral tetradentate ligand co-
ordinating through both carbonyl oxygens and both azo-
methine nitrogens. In the perchlorate complex, one of the
perchlorate ions is coordinated bidentately while in the nitrate
and thiocyanate complexes two of the anions are coordinated
monodentately to the metal ion. In the chloride and bromide
complexes, two of the halide ions are coordinated. A high-
spin octahedral geometry is assigned around Fe(III) in all of
these complexes.
*Corresponding author. E-mail: mgu@md2.vsnl.net.in
1663
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

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MADHU AND RADHAKRISHNAN
INTRODUCTION
Because of their di€erent coordination possibilities and, consequently,
their ¯exible complexing behaviour, the synthesis and structural investiga-
tions on pyrazolone-based ligands and their metal complexes have attracted
the attention of many investigators1,2. Iron complexes were the earliest
metal compounds studied in medicinal chemistry. They were and are used to
treat hypochromic anemia caused by iron de®ciency3. In view of this and as
part of our earlier investigations478 on metal complexes of pyrazolone de-
rivatives, we report here the synthesis and characterization of iron(III)
complexes of a Schi€ base ligand which is a pyrazolone derivative (Fig. 1).
RESULTS AND DISCUSSION
The formation of the complexes may be represented by the general
equation shown below.
FeX3 ‡ L ! FeꢀL†X3 ꢀX ˆ ClO4; NO3; SCN; Cl or Br†:
The complexes are dark brown solids, except the thiocyanate complex,
which is olive green. All of them except the thiocyanate complex are soluble
in acetonitrile, DMF, DMSO, ethanol, methanol and nitrobenzene, but
insoluble in benzene, chloroform, ethyl acetate and toluene. The thiocyanate
complex is soluble in DMF, DMSO and methanol, but insoluble in acetone,
acetonitrile, benzene, chloroform, ethyl acetate and nitrobenzene.
Figure 1. 1,2-Di(imino-40-antipyrinyl)ethane.

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1665
The elemental analysis data (Table I) suggest that the present com-
plexes may be formulated as: Fe(L)X3 (X ˆ ClO4, NO3, SCN, Cl or Br).
Electrical Conductance
The molar conductance values of the complexes (Table II) in acet-
onitrile, DMF, methanol and nitrobenzene are in the range expected for 1:2
electrolytes for the perchlorate complex9. The nitrate, thiocyanate, chloride
and bromide complexes behave as 1:1 electrolytes9. Thus, the complexes
may be formulated as [Fe(L)(ClO4)](ClO4)2 and [Fe(L)X2]X (X ˆ NO3,
SCN, Cl or Br).
Infrared Spectra
The important infrared spectral data of L and its complexes are pre-
sented in Table III. The band at 1650cm À1, characteristic of n(CˆO) of L, is
shifted to the region 159771630cm À1 in the complexes indicating the
coordination of both carbonyl oxygens6,7. Another intense band at 1576 cmÀ1
,
attributable to CˆN stretching in L, is shifted to the region 156071538 cmÀ1 in
the complexes indicating the coordination of both azomethine nitrogens7.
In the perchlorate complex, the triply-split band maxima at 1140, 1105
and 1020 cmÀ1 are due to the n8, n6 and n1 vibrations, respectively, of the
perchlorate ion of C2n symmetry, indicating the coordination of the per-
chlorate ion in a bidentate fashion7. But the band at 1085 cmÀ1 is assigned to
the n3 vibration of uncoordinated perchlorate of Td symmetry7. The
vibrational frequencies at 935 and 640cm À1 corresponding to the n2 and n3
vibrations, respectively, of the perchlorate (C2n) ion and the band at
625 cmÀ1 due to the n4 vibration of perchlorate (Td) ion, also support the
coexistence of both uncoordinated and bidentately coordinated perchlorate
ions in this complex7.
In the nitrate complex, two medium bands at 1430and 1315 cm À1 are
attributable to the n4 and n1 stretching vibrations, respectively, of the nitrate
ion of C2n symmetry10. Since n47n 1 is 115 cmÀ1, the nitrate ion is mono-
dentately coordinated10. A very strong band at 1380cm À1 and a medium-
intensity band at 820cm À1 are due to the n3 and n2 vibrations, respectively,
of uncoordinated nitrate ion (D3h)6,7
.
In the thiocyanate complex, a sharp band at 2050 cmÀ1 is in
accordance with the N-coordinated thiocyanate ion7. Further, the bands at
480cm À1 and 855 cmÀ1 stand as additional evidence for N-coordinated
thiocyanate ion7.

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MADHU AND RADHAKRISHNAN

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Table II. Molar Conductance Data of the Iron(III) Complexes of L (in ohmÀ1cm2
molÀ1
)
Molar Conductancea
Complex
C6H5NO2
CH3CN
288.08
DMF
144.04
CH3OH
180.68
[Fe(L)(ClO4)](ClO4)2
[Fe(L)(NO3)2]NO3
[Fe(L)(SCN)2]SCN
[Fe(L)Cl2]Cl
49.09
22.16
7
21.05
22.64
161.2077.56 .14
90
7
121.11
159.08
88.64
66.48
91.08
99.72
104.81
106.10
[Fe(L)Br2]Br
a10À3 M solutions.
In the far-infrared spectra of the halide complexes, the Fe-Cl and Fe-
Br stretching vibrations are at 313 and 285 cmÀ1, respectively7, which are
absent in the ligand spectrum.
The above spectral observations along with the conductance data in-
dicate that one of the perchlorates, two of the nitrates, thiocyanates,
chlorides and bromides are coordinated in these complexes. Further, the
n(Fe-O) and n(Fe-N) stretching vibrations are observed at about 555 and
460cm À1, respectively, in all of the complexes7,8
.
Electronic Spectra
The electronic spectral data of L and its complexes with the tentative
assignments are presented in Table IV. L shows two band maxima at
26,180cm À1 and 39,220cm À1 corresponding to the n ! pà and p ! pÃ
transitions, respectively7. In the complexes, the n ! pà bands are red-shifted
to the 25,309725,614 cmÀ1 region and the p ! pà bands are blue-shifted to
the 39,682740,322 cmÀ1 region compared to that of L. All of the complexes
exhibit a band in the 22,026723,509 cmÀ1 region corresponding to
the A1g ! EgꢀG† transition, consistent with octahedral Fe(III)11,12. Fur-
ther, all of the complexes exhibit an intense absorption band in the region
33,222733,333 cmÀ1, which might be due to a charge transfer transition.
6
4
Magnetic Moment Data
The molar magnetic moments of the complexes are presented in
Table IV. The values are in the range 5.8475.97 BM and suggest a high-spin
octahedral geometry around Fe(III) in these complexes13,14
.

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MADHU AND RADHAKRISHNAN

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Table IV. Electronic Spectral Data and Magnetic Moments of Iron(III) Complexes
of L
meff
(BM)
Abs. Max.
(cmÀ1
Tentative
Assignments
Compound
L
)
26,180n
39,220
! pÃ
7
p ! pÃ
[Fe(L)(ClO4)](ClO4)2
[Fe(L)(NO3)2]NO3
[Fe(L)(SCN)2]SCN
[Fe(L)Cl2]Cl
25,316
39,840
33,222
23,213
n ! pÃ
5.85
5.90
5.87
5.97
5.84
p ! pÃ
Charge transfer
4
6A1g ! Eg(G)
25,614
39,682
33,222
23,509
n ! pÃ
p ! pÃ
Charge transfer
4
6A1g ! Eg(G)
25,390n
40,322
33,333
22,026
! pÃ
p ! pÃ
Charge transfer
4
6A1g ! Eg(G)
25,390n
40,003
33,222
23,154
! pÃ
p ! pÃ
Charge transfer
4
6A1g ! Eg(G)
[Fe(L)Br2]Br
25,390n
40,001
33,222
23,213
! pÃ
p ! pÃ
Charge transfer
4
6A1g ! EgꢀG†
Based on the results of the present study, the structures shown in Fig. 2
may be assigned to the complexes.
EXPERIMENTAL
Materials
The metal salts were prepared from Analar ferric carbonate and the
respective 50% acids and crystallizing out the salts by evaporating the so-
lution on a steam bath. Ferric thiocyanate was prepared by the method
reported earlier15.

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MADHU AND RADHAKRISHNAN
Figure 2. Tentative structures of Fe(III) complexes of L.

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Preparation of the Ligand
The ligand, 1,2-di(imino-40-antipyrinyl)ethane (L) was prepared and
characterized as described previously6.
Preparation of Complexes
Perchlorate, Chloride, and Bromide Complexes
One mmol of Fe(ClO4)3Á6H2O (0.3628 g), FeCl3Á6H2O (0.2703 g) or
FeBr3Á6H2O (0.4036 g) in methanol (10 mL) was added to a boiling suspension
of 1.2 mmol of L (0.4294 g) in methanol (100 mL). This mixture was re¯uxed
for about 2 h on a boiling water bath. The dark brown solution obtained on
re¯ux was cooled and ®ltered. On evaporating the solvent to half of its volume
and subsequent cooling to room temperature, the complex separated, was
®ltered and repeatedly washed with hot ethyl acetate to obtain dark brown
solids of the pure complexes. Finally, the complexes were recrystallised from
methanol then dried under vacuum over phosphorus(V) oxide.
Nitrate and Thiocyanate Complexes
One mmol of Fe(NO3)3Á6H2O (0.3498 g) or Fe(SCN)3Á6H2O (0.3498 g)
in methanol (10mL) was added to a boiling suspension of 1.2 mmol of L
(0.4294 g) in ethyl acetate (100 mL). This mixture was re¯uxed for about 2 h
on a water bath. The precipitated complex was ®ltered and washed several
times with hot ethyl acetate to remove the excess ligand. Finally the com-
plexes were recrystallised from methanol and dried under vacuum over
phosphorus(V) oxide.
Physical Methods of Analysis
All the complexes were analyzed for metal and halide content by the
standard methods16. All other physical methods were the same as described
earlier7.
ACKNOWLEDGMENTS
We thank the Heads of the Regional Sophisticated Instrumentation
Centre, Indian Institute of Technology, Chennai, and the Central Drug

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MADHU AND RADHAKRISHNAN
Research Institute, Lucknow, for some instrumental analyses. We also
thank the Mahatma Gandhi University, Kerala, India, for the award of a
Junior Research Fellowship to one of us (NTM).
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Received May 6, 2001
Accepted August 18, 2001
Referee I: Z. Wu
Referee II: D. H. Williams

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